Shoes off in the house?

No one is allowed to walk thru our daycare in street shoes. Shoe covers are provided, but most remove their shoes. We all keep indoor shoes at work and put them on as soon as we enter the building. It's wonderful and no one complains. Our floors stay clean and the children are not exposed to all the street dirt/germs.

We always took the shoes off. Unfortunately, with beautiful California weather people feel like their shoes are clean. I asked few to take them off, but sometimes I feel strange to do it. But the whole time they are in my house, I keep thinking about their shoes. Once they leave, I go and clean.
I have new babysitter who did not take her shoes off and I saw pieces of dirt on my girl's nice rug. I think, I need to get one of those signs. Although, I kind of feel that you are either rude or oblivious when you do not see that my house is clean, I am wearing socks, and there are shoes by the door.
I always take shoes off in other people's houses, although those that wear shoes in a house have very dirty floors as I later learned from the color of my socks. :|